Now nearly half of London's 202 delivery offices and two thirds of its postmen and women are taking part in the strike.

As talks broke up for the night, Communication Workers Union Deputy General Secretary Dave Ward described the meeting between union leaders and management as "constructive."

But later he reacted in anger to accusations by Royal Mail that staff had been intimidated into taking part in the unofficial action.

Roger Baynes, director of operations for Royal Mail South East, who has been heading negotiations, said he hoped the dispute could be resolved before they went to the conciliation service Acas on Monday.

Speaking on Channel 4 News he warned staff were being intimidated into joining the action.

"The vast majority of our employees don't want to be out on strike, they
don't want to lose money, they don't want to disrupt services to our
customers.

"But you have picket lines and they are scared for those reasons."

But Mr Ward told the BBC: "There is no truth whatsover in the suggestion that bullying and harassment is the major sticking point in the dispute."

He called for an independent investigation into any bullying allegations.

Instead he said the issues were working conditions and one delivery time.

Strikers' demands

The CWU has said the row is not about London weighting, but about attempts to force through changes in working conditions.

Staff in Cambridge, Swindon and Stoke-on-Trent went out on unofficial strike on Friday while in Filton, Bristol, workers staged a one-hour walkout at lunchtime.

WHERE IS THE DISRUPTION?

London services are extremely disrupted and people are advised not to post letters